The connection of aluminium stranded leads/conductors/cables to connection parts, for example cable terminals made from copper or other non-ferric metals, is known for example from EP 1 032 077 A2. In this method, a material welded connection between the contact part and the cable is produced by means of a sleeve, said connection being substantially free from air inclusions between the individual strands of the aluminium stranded lead in the weld node. The aluminium strands and the aluminium sleeve form in the weld region a homogeneous, sealed weld node at which substantially no electrolyte can pass into the welded connection, thereby preventing contact corrosion.
One disadvantage of the method known from EP 1 032 077 A2 is the fact that the joining partners must be rotationally symmetrical. This significantly limits the scope of use of the method known from the prior art, since the joining partners have to be rotated coaxially relative to one another in order to use a rotational friction welding method, which means that the joining partners themselves are substantially rotationally symmetrical or at least can be clamped rotatably in a rotational friction welding tool. Due to the high speeds of rotation during rotational friction welding, asymmetries in the plane of rotation of the joining partners lead to imbalances which may have a negative effect on the welding process. Furthermore, in the case of rotational friction welding, it is not possible to set the axial angle between the joining partners. The final position of the rotational friction welding tools relative to one another cannot be precisely defined, and therefore this may result in an axial displacement of the joining partners relative to one another. This may be undesirable from the process point of view. Furthermore, the use of a friction welding method is limited to cross sections or more than 35 mm2.
For this reason, the subject-matter was based on the object of providing a welding method with which aluminium stranded leads can be securely connected to connection parts in axially defined positions.
This object is achieved according to the subject-matter by a connection of an aluminium stranded lead to a connection part, comprising a stripped end of the aluminium stranded lead and a metal connection part which is materially connected (materially joined, materially fit) to the stripped end of the aluminium stranded lead, in which an end face of the stripped end of the aluminium stranded conductor is welded to the connection part by means of torsional ultrasonic welding. It has been found that, by means of torsional ultrasonic welding, a solid welded connection can be produced while avoiding air inclusions between the aluminium strands. In the case of torsional ultrasonic welding, the joining partners, namely the aluminium stranded lead and the connection part, are moved relative to one another by means of axial relative movements. The torsional movement of the joining partners relative to one another takes place in the ultrasonic range, for example at a frequency of 20 kHz or more. The joining partners are in this case rotated relative to one another in minimum amplitudes, for example 10-100 μm, preferably 20-40 μm or between 0.1° and 5°. Since the welding energy is introduced by torsional vibration of the joining partners, the weld surfaces no longer have to be rotationally symmetrical. Instead, different geometries of contact parts, such as rectangles, ovals or ellipses, can now be welded to one another. All that is required is that the connection part completely covers the end face of the aluminium strands of the aluminium stranded lead. Since in torsional ultrasonic welding the contact parts may also be bent sheet-metal parts, it is possible to replace the contact parts which are conventionally used in rotational friction welding, such as expensive forged cable terminals for example, by inexpensive bent sheet-metal parts.